Im more trying to create or find Film grain simulation.
So the options of choosing different film types in the NIK Silver Efex Pro software (as Mike G. suggested) doesn't quite do it for you then?
For me, it's a good "near miss" emulating some of the more popular B&W films. Are you worried about the pretty decent generic kind of OK grain patterns? IMO it is probably 80% of ideal, which is actually "good enough" for most things, but I agree its not perfect. Usually the default results are "not quite enough" or "way too much". Does that make sense?
So what to do? For one of my personal projects in 2011, I have shot film and then scan the negs. I have also scanned a few transparencies but I am not first and foremost a slide shooter ;-)
Whatever, even doing that has its issues, but once you get the workflow set up, the results are probably 90% or more of ideal. I think the files I end up with are pretty darn good. Of course, you could always just develop and print the film using a 'real' darkroom, but if that's not possible...